Device for selecting automatically one from at least three hydraulic receiver circuits

ABSTRACT

This invention relates to devices for automatically selecting one hydraulic receiver circuit from at least three such circuits in a programmed order. According to the invention, the piston of an actuating jack is extended by two rods projecting from each side thereof and this assembly is interposed between two stops so that its travel in the two directions is limited to a length proportional to the step of the movable element of a distributor. One of these rods is connected to a resilient return member and the second of said two rods contains a step by step device for connecting it momentarily with the movable element of the distributor. The step by step device comprises a coupling piston slidably mounted in the cylinder of the second rod and also comprises at least one coupling member guided freely along a substantially radial direction.

United States Patent Michel L. Ribier Bruges, Gironde, France June 2,1969 Jan. 19, 1971 Derruppe S.A.

Le Bouscat-Bordeaux(Gronde), France a French company Inventor Appl. No.Filed Patented Assignee DEVICE FOR SELECTING AUTOMATICALLY ONE FROM ATLEAST THREE HYDRAULIC RECEIVER CIRCUITS Primary Examiner-Alan Cohan92/29X l37/624.l8

Attorney-Spencer and Kaye ABSTRACT: This invention relates to devicesfor automatically selecting one hydraulic receiver circuit from at leastthree such circuits in a programmed order. According to the invention,the piston of an actuating jack is extended by two rods projecting fromeach side thereof' and this assembly is interposed between two stops sothat. its travel in the two directions is limited to a lengthproportional to the step of the movable element of a distributor. One ofthese rods is connected to a resilient return member and the second ofsaid two rods contains a step by step device for connecting itmomentarily with the movable element of the distributor. The step bystep device comprises a coupling piston slidably mounted in the cylinderof the second rod and also comprises at least one coupling member guidedfreely along a substantially radial 73,290,993 12/1966 Clements 92/29Xdirection.

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a 46.1462 464 1 2o 1 22 26 y I i 1 24 1/ h 73 il 4o 25 24 a Q 5 4 4 6 s55 a9 a so 434 n ,4 8 27 --IL/---- 4 a (I 65 PATENTED JAN 1 9 |97|Inventor Michel. L- Riba'cr Attorneys a I l DEVICE FOR SELECTINGAUTOMATICALLY ONE FROM AT LEAs 'TnnEE HYDRAULIC RECEIVER CIRCUITS,

In numerous branches of technology it is desired to connectautomatically one aftertheother hydraulic receiver circuits in apredetermined succession or in a reverse succession according to whetherthe command signal is given by one or other of two pilot circuits. Thisrequirement may relate to power circuits for an hydraulic motor,sequential'circuits of a press, chain transfer or the like, hydrauliccircuits for controlling the change of speeds in a gear box, etc.

The present invention has for anobject to provide for this automaticselection a simple, strong, safe and efficient device which is easy toproduce, to'regulate and to maintain and whose cost is'relatively low.

In this device there is present, which'is already known for manualcontrols, a distributor comprising twomembers of which one is movablewith respect to'the other. These memher: have recesses which, accordingto the position which the movable member is occupying, allow'one of atleast three receiver circuitsto be connected to an hydraulic controlcircuit, and the otherreceiv'er circuit to a return circuit. The

movable member also cooperates with a resilient locking member whichacts to immobilize the said movable member in each oneof the positionswhich it is likely to occupy. l

The invention relates more particularly'in order to achieve the objectmentioned, to an actuating device sensitive to two pilot signals andconnected kinetically to the movable member of thedistributor in orderto move it."

In accordance with theinvention this actuating device comprises a jackwhose piston,drawn backzto a median position by a resilient member,separates in the cylinder two chambers connected to two hydraulic pilotcircuits and cooperates with twostop's limiting'its travel inbothdirections toa length proportional to the step of this movable member, amomentary connecting member being interposed between the said movablemember and the piston of the actuating jack, said link memberbeing-controlled by another jack connected to the particular pilotcircuit in use.

According to an embodiment particularly useful in the case where themovable member of the distributor is a slide valve, the aforementionedmomentary link member is at least one finger guided relative to'thepiston rod of the driving jack, in a substantially radial direction andplaced between, on the one to the travel of the said actuating jack,thepiston rod of this latter being provided coaxially with a" coupling jackwhose cam'carrying piston cooperates on a face with a resilient memberand discharges on its other face into an hydraulic chamber connecting,through at least onenonretum member, with the two chambers of theactuating jack.

Moreover, the actuating jack cooperates with an automatic resettingdevice which preferably comprises a distributor capable of establishingby rolling contact, communication between the pilot circuit in use and areturn circuit, this distributor being controlledby a piston whose twostepped faces are disposed in two chambers which are normally insulatedthe one from the other by a valve connecting the said faces and whichare connected on the said pilot circuit in use, the first directly andthe second through the valve, this second chamber being also connectedto the said return circuit by a passage whose orifice is controlled bythe piston of the actuating jack in its median position, the controlpiston of the aforementioned distributor also cooperating with aresilient member calibrated to balance a lower pressure than that whichtriggers the coupling finger.

Various other characteristics of the invention will appear moreover fromthe specific description which follows.

An embodiment of the object of the invention is shown by way ofnonlimiting example in the accompanying drawing the single FIG. of whichshows the device in longitudinal section.

The actuating or driving device described hereinafter with reference tothe drawing is applied in anonrestricting manner and only .to understandhow itoperates, to the control of a gear box with four gears andparticularly to that which was the object of the French Pat. No.1,513,369 of 23rd Nov. I966, in the name of Societe Anonyme Deruppe S.A.Of course the driving device according to the present invention can beused to control any box with more than three speeds and more generallyany mechanism, machine or other apparatus in which it is necessary tosupply selectively hydraulic receiver circuits as, for example, thosewhich are detailed hereinafter.

Moreover, this driving device cooperates for the selection of thecircuits with a distributor 1 which may be of any type and it is forthis reason that the distributor is not shown in detail in the drawingbut only outlined so as to show only the members which are necessary topractice the invention. The distributor may be of the turning or slidingtype.

The distributor chosen as an example comprises a body 2 in which isarranged a slide valve 3. The body 2 is connected to the four hydraulicreceiver circuits causing the changing of the four speeds of the box. Inthe case where this latter is that described in the aforementionedFrench Pat. No. 1,513,369, each" of the said receiver circuits suppliesthe jacks of two brakes, the body 2 is also connected to an hydrauliccontrol circuit supplying fluid under pressure and to a return circuitfeeding the fluid to a tank in which the pump sucks to pressurize thefluid supplied by the control circuit. The body 2 and the valve 3 havein a known manner internal grooves, holes or channels distributed insuch a way that to each of the four possible positions of the valve, thecontrol circuit is connected to one of the receiver circuits and thatthe return circuit communicates with the three other receiver circuits.These different positions of the valve are separatedwith respect to oneother by the same length or step p.

\ The valve 3 cooperates with a'loclting member allowing it to beimmobilizedin each of the four positions which it is likely to occupy.In the embodiment shown, this locking member is formed by two balls 4mounted in opposition to each other in a diametric hole 5 of the valve,and between which a spring 6 is placed to separate them resiliently fromeach other. Each of these balls cooperates selectively with fourrecesses 7.1, 7.2,

7.3 and 7.4 arranged in a hollow in the body 2 or in amember 8 arrangedin this latter. It is important to notice that these recesses 7.1 to 7.4are equidistant from each other and that their pitch p is equal to thatof the four possible positions of ,thetvalve. Advantageously, thelocking member thus constituted is accessible and to this end may besituated between a free end of the valve 3 and a removable cap of thebody 2.

The driving device of the invention is arranged in kinematic place thislatter step-by-step in one direction or the other according to whetherit is ordered by one pilot signal or another.

This device comprises a piston 10 arranged to slide in a cylindricalbore 11 of a box 12 arranged on the body 2 of the distributor. Thispiston is integral with coaxial rods 13 and 14 of the same diameterMoreover, its extreme faces, which are annular in shape since theysurround the said rods, are situated in chambers 15 and 16 of the boxwhich are permanently connected by any appropriate means to the twopilot circuits 17 and 18 respectively. Moreover, the annular faces ofthe pistons 10 cooperate with the ends l9and 20 of said chambers 15 and16, these ends effectively forming'stops. It should be observed that ifthis piston occupies the median position shown on the drawing, the pathwhich it may follow in one direction or the other is limited, by contactwith the stops 10 and 20, to a value equal to the pitch p of thepositions of the valve 3. v I

In order to draw back the said piston 10 in the medium position a spring21 is provided. It is placed between two washers or rings 22 and 23arranged to slide on an extension 24 of the piston rod 14 betweentwostop members integral with this extension and formed by a shoulder and aring usually called a circlip. These washers are arranged to rest onstop members 25 and 26 of the box 12 and its cap 27.

The path of the piston instead of being limited by contact with the ends19 and 20, may be limited by mutual abutment of the washers 22 and 23;in this latter case a cross tube of a suitable length may be placedbetween the said washers.

Under these conditions, if the piston 10 under the influence of thehydraulic pressure prevailing in the chamber 16 slides in the directionof the arrow F, it takes with it the washer 23 by the circlip of theextension 24 and compresses the spring 21 because the washer 22, beingapplied against the stop member 25, remains stationary. As soon as thepiston 10 is no longer controlled by the hydraulic fluid, the spring 21expands and draws it back. When the washer 23 is in contact both withthe stop member 26 and the extension circlip 24, and when the washer 22is in contact both with the stop member 25 and the shoulder of the saidextension, the piston 10 is in the median position. Similarly, if thepiston 10 under the influence of the hydraulic pressure prevailing inthe chamber slides in the opposite direction to that of the arrow F, ittakes with it the washer 22 by the shoulder of its extension 24 andcompresses the spring 21 against the washer 23 held immobile by the stopmember 25. As described hereinbefore, as soon as the piston is no longercontrolled by the hydraulic pressure, the spring 21 expands and draws itback towards its median position in which the washers 22 and 23 aresupported on the stop member of the extension 24 and also on the stopmember of the corresponding box 12.

1t thereby results that if the pilot conduit 18 is supplied, the piston10 is displaced in the direction of the arrow F and after the droppingpressure, the spring 21 draws back the said piston in to its medianposition. It is the same if the pilot conduit 17 is supplied instead ofthe conduit 18 but in this case the piston 10 slides in the oppositedirection to that of the arrow F.

As will be understood from the foregoing, a kinematic link isestablished between the valve 3 of the distributor l and the piston 10in such a way that the movement of the latter is communicatedstep-by-step to the said valve. For this purpose the rod 13 of thepiston 10 penetrates into the tubular end 28 situated opposite the valve3 and bears a screw coupling jack 29 connected to the pilot circuit 18or 18 in use.

In the embodiment shown in the drawing, this jack comprises a piston 30mounted to slide in a cylindrical bore 31 of the rod 13. One of thefaces of the piston 30 enters an hydraulic chamber 32 connectedpermanently, due to internal conduits 23 of the actuating or drivepiston 10, to an intermediate chamber 34 arranged in the box 12 betweenthe aforementioned chambers 15 and 16.

It is necessary for the chamber 32 not only to be connected to the pilotcircuit in use but it must be isolated from the other pilot circuit. Forthis purpose, the intermediate chamber 34 is connected to end chambers15 and 16 by one or more appropriate members which may be formed forexample by two nonretum valves or, as can be seen on the drawing, by aselection valve 35. This latter is mounted to slide in a cylindricalbore 36 of the box 12 in which the three chambers 15 and 16 and 34 lead.The end faces of the valve 35 are subjected to the pressures prevailingin the chambers 15 and 16, i.e. in the pilot circuits l7 and 18.Moreover, this valve is extended coaxially by cruciform stop heads 37and 38 arranged to limit its travel.

. Finally;-the length of the said valve is determined in such a way thatin an end position it frees a passage across a part of thebore 36 toestablish communication between the interi'nediate chamber 34 and theend drive chamber opposite this position, although it cuts offcompletely the other part of the bore 36 to isolate this intermediatechamber 34 from the other end chamber.

Thus, when the pilot circuit 18 for example is put into use, thehydraulic fluid pushes the valve 35 back to the position shown on thedrawing and from then on this fluid exists not only in the chamber 16but also in the intermediate chamber 34 and, through the conduits 33, inthe coupling chamber 32, although this fluid may not enter into theguide chamber 15 since it is prevented from doing so by the selectionvalve 35. in other words, this latter forms a member selectingautomatically the connection of the chamber 32 to the pilot circuit inuse.

The coupling piston 30 cooperatesn oreqver by its opposite face with aspring 39 bearing on a washer 4 0 immobilized in the rod 13 by means ofa ring 41 referred to as a circlip. The spring 39 tends to draw backthis piston to the position of disengagement shown on the drawing, inwhich,the,hydraulic fluid contained in the chamber 32 is withoutinfluence.

This piston is intended to establish the aforementioned kinematic linkbetween the drive rod 13 and the valve 3. To this end, at least onecoupling finger, guided relative to the rod 13 in a substantially radialdirection, is interposed between a cam of the said jack 30 and notchesof the same number as the locking recesses 7 in the said valve 3.

According to the embodiment shown on the drawing, two balls 42 acting aslocking fingers are lodged in the holes 43 of the tubular part of therod 13, these holes being situated opposite a groove 44 of the piston 30when this latter is in the disengaged position. The groove 44 iscircumscribed on the side of the chamber 32 by a conical wall 45 formingthe notch, so that if the said piston slides in the direction of thearrow F with respect to the rod 13, the cam 45' pushes back the balls 43towards the exterior and this causes them to project. On the other hand,if the piston is drawn back by the spring 39,to the disengaged position,the balls 42 may disappear completely, penetrating to the end of thegroove 4. These balls are capable of cooperating with anyone of thecircular grooves 46.1 to 46.4 hollowed out in the tubular end 28 of thevalve 3. These grooves are, in the embodiment shown, wherein thedistributor 1 controls four circuits, four in number, and aredistributed uniformly at the same pitch p as the locking recesses 7.1 to7.4. Moreover, the said grooves are V-shaped in profile so as to allowan easier release of the balls 42 then exist for the balls 4 outside therecesses 7.

The selection valve 35 allows the pilot circuit 17 or 18 in use to beconnected not only to thecorresponding actuating or drive chamber 15 or16 and to the coupling chamber 32, but also to a chamber 47 of anautomatic resetting device 48 described hereinafter. This device allowsa single cycle of operation to be completely controlled (i.e. theadvance by one step in one direction or the other of the valve 3 and thereturn to the initial position of the deviceaccording to the invention)and will now allow the carrying out of another subsequent cycle. inother words, this device allows the execution of successive selectionsto be timed which occurs when the information transmitted by the pilotcircuit in use persists.

The device 48 comprises a distributor 49 constituted by a cylindricalvalve mounted to slide in a recess 50 of the box 12. in this latter arearranged two annular grooves 51 and 52, the first of which is connecteddirectly to the intermediate chamber 34 and the second of which isconnected to the return circuit of the hydraulic installation. At rest,i.e. in the position shown on the drawing, the distributor valve 49obturates the groove 42 so that the pressure in the pilot circuit in useand the recesses to which it is connected may increase. But this valve49 is capable of establishing, when it is shifted in the oppositedirection to that of the arrow F, by an annular recess 53 hollowed outin its periphery, communication between the grooves 51 and 52 and as aresult, the pilot circuit in use and the cavities to which it isconnected are connected to the return circuit which has the effect ofproducing a decrease in pressure.

The distribution valve 49 is extended by a piston head 54 having twostepped faces 55 and 56 connected by a valve holder 57. This valveholder cooperates usually, i.e. in the position shown on the drawings,with a seat of a member 58 bordering the aforementioned chamber 47 whichis circumscribed by the said member. This latter is connected in asealed manner in the box 12 and immobilized by any appropriate means. Ofcourse, this member may be removed and replaced by a complete part ofthe box 12. The valve 57 isolates the chamber 47 referred to as thecentral chamber, from a peripheral chamber 59 arranged in the recess 50between the face 55 of the piston 54 and the face situated opposite themember 58.

Moreover, the central chamber 47 is connected, by internal conduits 60from the piston 54 which lead into the annular recess 53 of the valve49, to the intermediate chamber 34. in these conditions the centralchamber 47 is connected permanently to the pilot circuit in use underthe control of the selection valve 35 as is already the case for thecoupling chamber 32.

Moreover, the peripheral chamber 59 is itself connected to the returncircuit for the hydraulic fluid but in a temporary manner. in fact, itneed only be connected when the piston is in the median position shownon the drawing. Consequently, communication between the peripheralchamber 59 and the return circuit is controlled by the said piston. inthe embodiment shown on the drawing, the rod 13 of the piston 10 isarranged to slide in a recess 61 of the box 12 which has two chambers 62and 63. The chamber 62 communicates permanently with the return circuitthrough an orifice 62a and the chamber 63 with the peripheral chamber 59by a conduit 64 and a circular groove 65 of the box 12 as well aslongitudinal grooves 66 of the member 58. The valve 13 has, finally, agroove 67 opposite the part of the bore 61 between the chambers 62 and63 when the piston is in the median position shown on the drawing, thisgroove being longer than the said part. Consequently, the groove 56establishes connection between the chambers 62 and 63, i.e. finallybetween the peripheral chambers 59 and the return circuit, only when thepiston is ina median position; on the other hand, when this latteroccupies any one of its end positions, the rod 13 shuts oh the part ofthe bore 61 between the chambers 62, 63 and thus isolates these latterfrom each other, consequently closing the peripheral chamber 59.

The distributor valve 59 is under the influence not only of the pressureof hydraulic fluid filling the central chamber 47 and eventually theperipheral chamber 59 but also of an opposing spring 68 bearing on thecap 27. This spring is calibrated to balance a pressure P applied onboth faces 55 and 56 of the piston head 54. In other words, when thechambers 47 and.59 are in communication the pressure existing in thesetwo chambers being the same as that set up in the pilot circuit in use,the spring 68 acts on the valve 49 to build up the said pressure and tomaintain it equal to P In fact, if this pressure is higher than l thevalve 49 operates to establish connection between the grooves 51 and 52by its recess 53, i.e. between the pilot circuit in use and the returncircuit. On the other hand, if this pressure becomes slightly less thanP the valve 49 returns and shuts off the groove 52 thus isolating thepilot circuit from the return circuit. in these conditions the valve 49is submitted to the opposing forces of the spring 68 and of thehydraulic pressure applied to the faces 55 and 56, stabilizes the saidpressure while keeping it at P by passing the hydraulic fluid betweenits recess 53 and the groove 52.

Moreover, it is important to note that the face 56 has a smaller surfacethan the total section of the piston head 54 which allows the releasethreshold of the resetting device 48 to be determined.

in fact, when the valve 57 separates the central chamber 47 from theperipheral chamber 59, which although isolated from the return circuitby the rod 13 is at the pressure of this latter, the distributor 49isonly submitted to the counter actions of the spring 68 and of thehydraulic fluid in the chamber 47, which is at the pressure of the pilotcircuit. Given that this pressure is exerted on a reduced surface whichis that of the face 56, the valve 57 can only open when the saidpressure reaches a value P, higher than the aforementioned pressure PThis value is determined by the ratio of the surface of the face 56 andof the total section of the piston 54. Under these conditions, as soonas the pressure in the pilot circuit reaches the value P, the valve 57opens and the said pressure is applied intermediately on the other face55 of the piston 54. The instantaneous application of the pressure on anincreased surface has the effect of possibly displacing the valve 59which establishes through this force a connection between the said pilotcircuit and the discharge circuit. The pressure lowers rapidly, but isstabilized at the value P by the intervention of the spring 68.

The spring 21 is calibrated to balance, in the chambers 15 and 16 of theactuating or drive jack, a pressure P lower than the aforementionedvalue P but higher than the value P ln a similar manner, the spring 39is calibrated to balance in the chamber 32 of the coupling jack, apressure P between the values P and P Finally, the spring 6 acting onthe locking balls 4 of the valve 3 in the body 1 is calibrated to causea force such that the locking obtained can resist the release force ofthe coupling balls 42 when the piston 30 is subjected to an hydraulicpressure P but gives way when the balls 42 are interlocked and transmitthe thrust of the traction of the actuating or drive piston 10 subjectedto a pressure P The automatic selection device according to theinvention as has been described hereinabove, operates as will bedescribed hereinafter. The pilot circuits [7 and 18 being assumed not tobe transmitting any information, the various members of the deviceoccupies the positions appearing on the drawing.

lf hydraulic fluid is discharged into the pilot circuit 18, it appearsdirectly in the actuating or drive chamber 16 and through the passagefreed by the selection valve 35, in the coupling chamber 32 and thecentral resetting chamber 47. Of course, if the valve 35 were to occupypreviously the position opposite to that shown on the drawing, thehydraulic fluid would cause its displacement to free the aforementionedpassage.

The pressure in the chambers 16, 32 and 47 increases and when it reachesthe value P the hydraulic fluid pushes the piston 30 in the direction ofthe arrow F against the action of the spring 39. At the time of thisdisplacement the cam 45 acts on the balls 42 and engages them stronglyin the groove 46.2. in this first time, the coupling of the drive piston10 with the valve 3 is thus produced.

The pressure of the hydraulic fluid in the said chambers 16, 32 and 47continues to grow and when it reaches the value P the hydraulic fluidinduces, against the action of the spring 21, the displacement of theactuating or drive piston 10 in the direction of the arrow F, whichconsequently, drives the valve 3 in the same direction, since thelocking device 4, 6 gives way when the coupling device resists. When thepiston 10 arrives at the end of its travel, i.e. when it abuts the base10, the balls 4 are situated opposite the recess 7.3 into which they arethen interlocked automatically under the action of the spring 6.

The pressure in the chambers 16, 3 2 and 47 continues yet again toincrease and when it reaches the value P the hydraulic fluid causes thevalve 57 to open, which thus establishes a connection between thechambers 47 and 59. Given that the connection between this chamber 59and the return circuit is interrupted by the rod 13 closing the passagebetween the chamber 62 and 63, the pressure P;, prevailing in the twochambers 47 and 59 is thus applied over all the section of the piston54. The distributor valve 49 thus shifts forcibly in the oppositedirection to that of the arrow F against the action of the spring 68.The recess 53 then connects the grooves 51 and 52 and as a result ofwhich the pilot circuit in use 18 as well as the chambers 16, 32, 47 and59, are connected to the return circuit. The pressure drops and when itbecomes equal to the value P it stabilizes, given that the valve 49under the counteractions of the spring 68 and of this pressure, occupiesa position of stable equilibrium in which the grooves 51 and 52communicate through a small passage causing a flow of the fluid.

The aforementioned drop in pressure is practically instantaneous. Thelocking device 4, 6 resists and holds the valve 3 during the executionof the following action. The actuating of drive piston 10, under theaction of the spring 21, which has become preponderant, returns to themedian position shown on the drawing. At the beginning of this returnaction, the balls 42 escape under the combined action of the traction ofthe rod 13, of the thrust of the spring 39 and of the reaction of theinclined ramp of the groove 46.2. The rod 13 is thus uncoupled from thevalve 3. During this return action, the hydraulic fluid forced back fromthe chamber 16 and 33 by the pistons and 13 respectively, is evacuatedto the return circuit by flowing between the recess 53 of the valve 49and the groove 52 but the hydraulic pressure remains equal at the valueP under the influence of the spring 68. At the end of the travel of thepiston 10, the groove 67 of the rod 13 connects the peripheral chamber59 to the return circuit and from then on the pressure on the faces 55and 56 of the piston 54 is canceled. The spring 68, no longer beingbalanced by the pressure P pushes back the valve 49 and closes thecentral chamber 47 by the valve 57. All the members of the device arereturned to their initial position but the balls 42 are situatedopposite the groove 56.3. The device is thus available for a newselection cycle and will act as soon as one of the pilot circuits 17 and18 is put into use. if the pilot circuit 18 has remained in use withoutinterruption, a new selection cycle is executed as soon as the valve 56is closed.

Of course, the operation of the device during one cycle is the same asdescribed hereinabove if the pilot circuit 17 is put into use instead ofthe pullout circuit 18. The only difference resides in the fact that theactuating or drive piston 10 is displaced in the opposite direction tothat of the arrow F and transmits in the same direction the displacementby one step to the valve 3.

The embodiment of the device according to the invention describedhereinabove is particularly interesting because the various members usedare easy to execute to make it fit and to adjust. There are, moreover,integrated into a compact unit to which only three connections have tobe provided for the two pilot circuits and the return circuit. Moreover,the operation of this device is certain and efficient.

Nevertheless there is nothing to prevent certain of the members beingreplaced by other members which have an equivalent function. Moreparticularly, the selection valve 35 may be replaced by two nonretumvalves arranged in the pilot circuits l7 and 18; the automatic resettingdevice 48 may be replaced by a time-controlled closing member for thetwo pilot circuits l7 and 18, controlled by the actuating or drivepiston 10 when it arrives to its end of travel positions. Moreover, inthe case where the valve 3 of the distributor 1 is of the rotary type,the coupling device 29 may be replaced by another equivalent, but whichcomprises in addition a member transforming the translation movement ofthe piston 10 into a movement of rotation.

The invention is not limited to the embodiment shown and described indetail, since various other modifications may be arranged withoutdeparting from its scope.

1 claim:

1. in a device for automatically selecting individually one hydraulicreceiver circuit from at least three such circuits in a programmedorder, applicable particularly to the selective speed control of a gearbox having at least three speeds, and comprising a distributor which isdisposed between said three receiver circuits and a hydraulic controlcircuit, and of which the movable element, capable of occupying at leastthree equidistant positions of the same step cooperates with a resilientintervening locking member for each of them and also with an actuatablejack having two chambers separated by a piston, said chambers beingconnected to two pilot circuits indicating the selection of the receivercircuits in one direction or in the-other, said jack being connected tosaid movable element by a stepping device, the improvement whichconsists in that the piston of the actuating jack is extended coaxiallyby two rods extending from each side thereof, the assembly thusconstituted between interposed two stops limiting its travel in the twodirections to a length proportional to the step of the movable elementof the distributor, a first one of said two rods being connected to aresilient member for return towards the median position the second oneof said two rods containing the said step-by-step device inthe saidmovable tended for connecting it momentarily wit element, and whereinsaid step-by-step device comprises a coupling piston slidably mounted inthe cylinder of said second rod and of which a face extends into anhydraulic cylinder communicating, by means of an automatic selectormember such as a slide valve, with that chamber of said actuatinghydraulic jack that is connected to the pilot circuit in operation,while the other face of said coupling piston is supported by a resilientreturn member, and wherein said step-bystep device also comprises atleast one coupling member guided freely along a substantially radialdirection, in the second said rod and interposed between a cam of saidcoupling piston and any one of at least three notches having automaticescapement, provided in a part of the movable element of saiddistributor with a step equal to the travel of the actuating hydraulicjack from its median position.

2. A device according to claim 1, that comprises, in combination, anautomatic resetting device that comprises an auxiliary distributor,constituted by a piston slidably mounted in a cylinder of which a firstgroove and a second groove cooperating with a third groove of saiddistributor piston to produce by throttling, when sliding, a drop inpressure of the pilot fluid, and wherein the distributor is supported atone end of a resilient member and has, at its other hand, two steppedfaces situated in two chambers which are normally isolated one from theother by a valve, and wherein said second chamber is also capable ofbeing connected to the said return circuit under the control of theactuating piston in its median position only, by means of groovesprovided in said second rod of said actuating piston and in a guidingcylinder of the latter.

3. A device according to claim 2, wherein said resilient membercooperating with said coupling piston is adjusted to balance a hydraulicpressure lower than that which balances the adjusting of the resilientmember attracting said piston of said actuating hydraulic jack, andwherein the resilient blocking member of said movable element of saiddistributor is calibrated to resist the disappearing force of thefastening member of this movable element with said first rod of saidactuating hydraulic jack but to yield to the force of the latter, andwherein said resilient member attracting the resetting piston iscalibrated to balance a pressure exerted on its two stepped faces whichis lower than that which triggers the fastening member.

1. In a device for automatically selecting individually one hydraulicreceiver circuit from at least three such circuits in a programmedorder, applicable particularly to the selective speed control of a gearbox having at least three speeds, and comprising a distributor which isdisposed between said three receiver circuits and a hydraulic controlcircuit, and of which the movable element, capable of occupying at leastthree equidistant positions of the same step cooperates with a resilientintervening locking member for each of them and also with an actuatablejack having two chambers separated by a piston, said chambers beingconnected to two pilot circuits indicating the selection of the receivercircuits in one direction or in the other, said jack being connected tosaid movable element by a stepping device, the improvement whichconsists in that the piston of the actuating jack is extended coaxiallyby two rods extending from each side thereof, the assembly thusconstituted between interposed two stops limiting its travel in the twodirections to a length proportional to the step of the movable elementof the distributor, a first one of said two rods being connected to aresilient member for return towards the median position the second oneof said two rods containing the said step-by-step device intended forconnecting it momentarily with the said movable element, and whereinsaid step-by-step device comprises a coupling piston slidably mounted inthe cylinder of said second rod and of which a face extends into anhydraulic cylinder communicating, by means of an automatic selectormember such as a slide valve, with that chamber of said actuatinghydraulic jack that is connected to the pilot circuit in operation,wHile the other face of said coupling piston is supported by a resilientreturn member, and wherein said step-by-step device also comprises atleast one coupling member guided freely along a substantially radialdirection, in the second said rod and interposed between a cam of saidcoupling piston and any one of at least three notches having automaticescapement, provided in a part of the movable element of saiddistributor with a step equal to the travel of the actuating hydraulicjack from its median position.
 2. A device according to claim 1, thatcomprises, in combination, an automatic resetting device that comprisesan auxiliary distributor, constituted by a piston slidably mounted in acylinder of which a first groove and a second groove cooperating with athird groove of said distributor piston to produce by throttling, whensliding, a drop in pressure of the pilot fluid, and wherein thedistributor is supported at one end of a resilient member and has, atits other hand, two stepped faces situated in two chambers which arenormally isolated one from the other by a valve, and wherein said secondchamber is also capable of being connected to the said return circuitunder the control of the actuating piston in its median position only,by means of grooves provided in said second rod of said actuating pistonand in a guiding cylinder of the latter.
 3. A device according to claim2, wherein said resilient member cooperating with said coupling pistonis adjusted to balance a hydraulic pressure lower than that whichbalances the adjusting of the resilient member attracting said piston ofsaid actuating hydraulic jack, and wherein the resilient blocking memberof said movable element of said distributor is calibrated to resist thedisappearing force of the fastening member of this movable element withsaid first rod of said actuating hydraulic jack but to yield to theforce of the latter, and wherein said resilient member attracting theresetting piston is calibrated to balance a pressure exerted on its twostepped faces which is lower than that which triggers the fasteningmember.